Battery Pack with Segmented, Electrically Isolated Heat Sink

ABSTRACT

A battery assembly is provided that utilizes electrically isolated heat sinks to enhance battery pack thermal management and safety. The battery assembly is divided into groups of batteries, where the batteries within each group are of the same voltage, and where each battery group is serially coupled to the other battery groups. The heat sink is segmented, where each heat sink segment is thermally coupled to the batteries within a single battery group, and where each heat sink segment is electrically isolated from the adjacent heat sink segments. The heat sink segments are thermally coupled to a cold plate, and electrically isolated from the cold plate by a layer of a thermal interface material.

FIELD OF THE INVENTION

The present invention relates generally to batteries and battery packsand, more particularly, to a system that improves battery pack safety.

BACKGROUND OF THE INVENTION

In response to the demands of consumers who are driven both byever-escalating fuel prices and the dire consequences of global warming,the automobile industry is slowly starting to embrace the need forultra-low emission, high efficiency cars. While some within the industryare attempting to achieve these goals by engineering more efficientinternal combustion engines, others are incorporating hybrid orall-electric drive trains into their vehicle line-ups. To meet consumerexpectations, however, the automobile industry must not only achieve agreener drive train, but must do so while maintaining reasonable levelsof performance, range, reliability, safety and cost.

In recent years there have been several incidents of a rechargeablebattery pack, contained within a laptop computer or utilized in avehicle, catching on fire. As a result, one of the primary issuesimpacting consumer confidence with respect to both hybrid andall-electric vehicles is the risk of a battery pack fire.

Rechargeable batteries tend to be relatively unstable and prone tothermal runaway, an event that occurs when a battery's internal reactionrate increases to such an extent that it is generating more heat thancan be withdrawn. Thermal runaway may be the result of a battery short,a manufacturing defect, improper cell use, or damage such as that whichmay be sustained during an accident or when road debris dents orpunctures the battery pack. If the reaction rate and the generation ofheat go unabated during the thermal runaway event, eventually thegenerated heat becomes great enough to cause the battery and materialsin proximity to the battery to combust. Therefore when the batteryundergoing thermal runaway is located within a battery pack containingtens or hundreds of batteries, a single event can quickly propagatethroughout the pack, dramatically increasing the likelihood of propertydamage as well as the risk to people in close proximity to the vehicle.

Vehicle manufacturers have employed a variety of techniques to bothminimize the risk of a battery undergoing thermal runaway and controlthe propagation of the event if one should occur. These techniquesinclude ballistic shields to prevent battery pack damage from roaddebris, monitors that detect battery malfunctions, monitors that detectthe onset of a thermal runaway event, and advanced thermal managementand fire control systems that help to limit event propagation. Whilethese techniques may reduce the likelihood of a thermal runaway eventand limit its effects when one does occur, until improvements inbatteries and battery chemistries completely eliminate such events,additional systems are required that can be used to further minimize therisk to people and property alike. The present invention provides such asystem.

SUMMARY OF THE INVENTION

The present invention provides a battery assembly comprised of (i) aplurality of batteries; (ii) a plurality of bus bars positionedproximate to a first end portion of each of the batteries andelectrically connected to the first and second terminals of each of thebatteries; (iii) a plurality of heat sink segments; (iv) a cold platethermally coupled to the plurality of heat sink segments; and (v) alayer of a thermal interface material interposed between the cold plateand the heat sink segments, where the thermal interface material isthermally conductive and electrically insulative. With respect to theplurality of batteries, the first end portion of each of the batteriesincludes both the first terminal and the second terminal. The batteriesare divided into a plurality of battery groups with each battery groupcomprised of a subset of the plurality of batteries, and with thebattery groups being electrically connected in series. The batterieswithin each subset are electrically connected in parallel such that eachsubset is maintained at a different voltage than the other batterysubsets. With respect to the plurality of heat sink segments, each heatsink segment is electrically isolated from the adjacent heat sinksegments. Each of the heat sink segments is thermally coupled to onebattery group of the plurality of battery groups such that a second endportion of each battery of each battery group is thermally coupled toone heat sink segment of the plurality of heat sink segments. The secondend portion of each battery is distal from the first end portion.

The assembly may be further comprised of a thermally conductive materiallayer (e.g., an epoxy, a ceramic, etc.) interposed between the secondend portion of each battery and the corresponding heat sink segment,where the thermally conductive material layer is electricallyinsulative. The thermally conductive material layer may be configured tocontact and be thermally coupled to the lower portion of each of thebatteries. The thermally conductive material layer preferably has athermal conductivity of at least 0.75 Wm⁻¹K⁻¹ and a resistivity of atleast 10¹² ohm-cm.

The assembly may be further comprised of an electrically insulativematerial interposed between each heat sink segment and the adjacent heatsink segments. The electrically insulative material interposed betweeneach heat sink segment and the adjacent heat sink segments preferablyhas a resistivity of at least 10¹² ohm-cm.

The assembly may be further comprised of at least one coolant conduitthermally coupled to the cold plate, where the coolant conduit(s) ispreferably coupled to a battery pack thermal management system. Thecoolant conduit(s) may be integrated into the cold plate, for exampleintegrated within apertures passing through the cold plate or withinslots located on a surface of the cold plate.

The layer of thermal interface material that is interposed between thecold plate and the heat sink segments preferably has a resistivity of atleast 10¹² ohm-cm. Preferably the thermal conductivity of the layer ofthermal interface material interposed between the cold plate and theheat sink segments is at least 0.75 Wm⁻¹K⁻¹, more preferably at least5.0 Wm⁻¹K⁻¹, and still more preferably at least 20.0 Wm⁻¹K⁻¹.

The heat sink segments may be comprised of metal (e.g., aluminum).Preferably the heat sink segments have a thermal conductivity of atleast 100 Wm⁻¹K⁻¹.

The cold plate may be comprised of metal (e.g., aluminum). Preferablythe cold plate has a thermal conductivity of at least 100 Wm⁻¹K⁻¹.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

It should be understood that the accompanying figures are only meant toillustrate, not limit, the scope of the invention and should not beconsidered to be to scale. Additionally, the same reference label ondifferent figures should be understood to refer to the same component ora component of similar functionality.

FIG. 1 provides a perspective view of a battery pack and the vehiclechassis to which it is to be mounted;

FIG. 2 is a schematic diagram of a battery assembly in accordance withthe prior art in which the bus bars are located above and below thebatteries;

FIG. 3 is a schematic diagram of a battery assembly in accordance withthe prior art in which the bus bars are adjacent to the positiveterminals of the batteries;

FIG. 4 is a detailed cross-sectional view of the bus bars in a layerstack in a manner similar to that shown in FIG. 3;

FIG. 5 is a perspective view of a battery holder that may be used withthe present invention;

FIG. 6 is a schematic diagram of a battery assembly similar to thatshown in FIG. 3, utilizing a different bus bar configuration;

FIG. 7 is a schematic diagram of the battery assembly of FIG. 6,modified to incorporate the heat sink assembly of the invention;

FIG. 8 provides a cross-sectional view of the lower portion of thebattery assembly shown in FIG. 7, this view taken along plane A-A ofFIG. 7;

FIG. 9 illustrates an exemplary cooling system suitable for use with abattery assembly such as that of the invention;

FIG. 10 illustrates an alternate exemplary cooling system suitable foruse with a battery assembly such as that of the invention;

FIG. 11 illustrates an alternate battery assembly to that shown in FIG.6, this embodiment incorporating the coolant conduit directly into theheat sink segments;

FIG. 12 provides a cross-sectional view of the lower portion of thebattery assembly shown in FIG. 11, this view taken along plane B-B ofFIG. 11;

FIG. 13 provides a cross-sectional view, similar to that shown in FIG.12, of an alternate conduit mounting arrangement;

FIG. 14 illustrates an alternate battery assembly to that shown in FIG.11, this embodiment eliminating the thermal interface between thecoolant conduits and the heat sink segments;

FIG. 15 provides a cross-sectional view of the lower portion of thebattery assembly shown in FIG. 14, this view taken along plane C-C ofFIG. 14;

FIG. 16 provides a cross-sectional view, similar to that shown in FIG.15, of an alternate conduit mounting arrangement; and

FIG. 17 provides a bottom view of a battery assembly in accordance withthe invention, this view illustrating the preferred orientation of thecoolant conduits relative to the heat sink segments.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises”, “comprising”, “includes”, and/or“including”, as used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. As used herein, the term “and/or” and the symbol “/” are meantto include any and all combinations of one or more of the associatedlisted items. Additionally, while the terms first, second, etc. may beused herein to describe various steps or calculations, these steps orcalculations should not be limited by these terms, rather these termsare only used to distinguish one step or calculation from another. Forexample, a first calculation could be termed a second calculation, and,similarly, a first step could be termed a second step, without departingfrom the scope of this disclosure.

In the following text, the terms “battery”, “cell”, and “battery cell”may be used interchangeably and may refer to any of a variety ofdifferent battery configurations and chemistries. Typical batterychemistries include, but are not limited to, lithium ion, lithium ionpolymer, nickel metal hydride, nickel cadmium, nickel hydrogen, nickelzinc, and silver zinc. The term “battery pack” as used herein refers toan assembly of one or more batteries electrically interconnected toachieve the desired voltage and capacity, where the battery assembly istypically contained within an enclosure. The terms “electric vehicle”and “EV” may be used interchangeably and may refer to an all-electricvehicle, a plug-in hybrid vehicle, also referred to as a PHEV, or ahybrid vehicle, also referred to as a HEV, where a hybrid vehicleutilizes multiple sources of propulsion including an electric drivesystem.

FIG. 1 provides a perspective view of a battery pack 101 configured tobe mounted under vehicle chassis 103. It should be understood that thepresent invention is not limited to a specific battery pack mountingscheme, battery pack size, or battery pack configuration.

FIG. 2 illustrates one configuration of a battery assembly 200 thatlocates bus bars both above and below the batteries. Typically in such aconfiguration, a cooling conduit (not shown) is positioned between thesides of the batteries, thereby providing a means of regulating batterytemperature. Although assembly 200 may be used with any type of battery,in the illustrated assembly batteries 202-212 are cylindrically-shaped,with a nub projecting from the top end of the cell serving as thepositive terminal and the can (also referred to as a casing) serving asthe negative terminal. Typically a portion of the negative terminal islocated at the top end of the cell, for example due to a casing crimpwhich is formed when the casing is sealed around the contents of thebattery. This crimp or other portion of the negative terminal at the topend of the cell provides physical and electrical access at the top endto the negative terminal of the battery. The crimp is spaced apart fromthe peripheral sides of the projecting nub through a gap that may or maynot be filled with an insulator.

In illustrated battery assembly 200, the batteries are divided into afirst group of batteries 202 and 204 that are connected in parallel, asecond group of batteries 206 and 208 that are connected in parallel,and a third group of batteries 210 and 212 that are connected inparallel. The first, second and third groups of batteries are connectedin series. Bus bars 214, 216, 218, 220, 222, 224 are used to connect thebatteries in this parallel and series coupling. Each of the bus bars iscoupled to the respective batteries with one or more wires. A relativelythick wire 226 couples the second bus bar 214 to the third bus bar 222,making a series connection between the first and second battery groups,while a second relatively thick wire 228 couples the fourth bus bar 216to the fifth bus bar 224, making a series connection between the secondand third battery groups. As a result, the first bus bar 220 is thenegative terminal while the sixth bus bar is the positive terminal forbattery assembly 200.

The use of bus bars at both ends of the batteries as illustrated in FIG.2 limits the area where a heat sink can be affixed to either end inorder to achieve efficient heat removal. Additionally, soldering orotherwise connecting the relatively thick wire (e.g., wires 226 and 228in FIG. 2) from an upper bus bar to a lower bus bar adds assemblycomplexity, and thus cost, to such a battery pack. Wires 226 and 228 canalso introduce parasitic resistance into the current path, which in turncan introduce a voltage drop under high current drain conditions.Lastly, wires 226 and 228 are subject to breakage, resulting in shortcircuits, open circuits, or other reliability problems.

FIG. 3 illustrates a battery assembly 300 utilizing an alternate bus barconfiguration in which all of the bus bars are proximate to one end ofthe battery assembly, thus enabling efficient heat removal from theother end of the battery assembly via heat sink 301. Heat sink 301,which may utilize either air or liquid cooling, is thermally coupled tothe bottom end portions 240 of each of the batteries, i.e., batteries202, 204, 206, 208, 210 and 212.

Access to both the positive and negative terminals in battery assembly300 is at one end of the cells, e.g., at the top end of the cells, wherethe bus bars are coupled to the positive and negative terminals usingwires. In addition to requiring fewer bus bars than in the configurationof assembly 200, this approach also allows the connecting wires to besignificantly shorter, and less resistive, than those required byassembly 200 (e.g., wires 226 and 228 that are used to connect the upperbus bars to the lower bus bars).

As shown in FIG. 3, the first group of batteries 202 and 204 areconnected in parallel and are of a first voltage, the second group ofbatteries 206 and 208 are connected in parallel and are of a secondvoltage, and the third group of batteries 210 and 212 are connected inparallel and are of a third voltage. The first, second and third groupsof batteries are connected in series. Bus bars 314, 316, 318, 322 areused to couple the batteries in this parallel and series arrangement.Specifically, starting with the negative terminal of battery assembly300, a first bus bar 314 is connected to the negative terminals of thefirst group of batteries 202 and 204 while a second bus bar 322 isconnected to the positive terminals of the same group of batteries 202and 204, both at the top end portion 238 of each of the batteries. Thefirst and second bus bars 314 and 322 couple the first group ofbatteries 202 and 204 in parallel. Similarly, the second bus bar 322 andthe third bus bar 316 couple the second group of batteries 206 and 208in parallel, while the third bus bar 316 and the fourth bus bar 318couple the third group of batteries 210 and 212 in parallel. Seriesconnections between battery groups are formed by the bus bars,specifically the second bus bar 322 connects the positive terminals ofthe first group of batteries 202 and 204 to the negative terminals ofthe second group of batteries 206 and 208; and the third bus bar 316connects the positive terminals of the second group of batteries 206 and208 to the negative terminals of the third group of batteries 210 and212. The fourth bus bar 318 is the positive terminal of the batteryassembly 300. It should be understood that other bus bar configurationsutilizing various combinations of parallel and serial connections may beused without departing from the approach of making all connections tothe top portions of each of the batteries.

In battery pack 300, the bus bars are arranged in a layer stack 350,although other configurations, such as those described below, may beused with the invention. In layer stack 350, the first bus bar 314 andthe third bus bar 316 are placed in a first layer 330, and are separatedby a gap to prevent short circuiting. In some embodiments the gap isfilled with an insulator. An insulator is disposed as the second layer332. The second bus bar 322 and the fourth bus bar 318 are placed in athird layer 334, and are separated by a gap or insulator to preventshort circuiting. The third layer 334 is separated from the first layer330 by the electrically insulating second layer 332 to prevent shortcircuiting. It should be understood that layer stack 350 is simply anexemplary stack and that alternate stack configurations are possible.For example, the layer stack may have more than three layers and eachbus bar layer may have a single bus bar or two or more bus bars disposedwithin a single co-planar layer.

The layer stack may be formed using layers of a circuit board. Forexample, the bus bars can be made of (or on) copper layers or anothersuitable conductive metal and the insulator can be made of resinimpregnated fiberglass or other suitable electrically insulatingmaterial. Alternately, the bus bars can be made of aluminum or otherelectrically conductive material with any of a variety of electricallyinsulating material applied as an insulating layer.

It will be appreciated that there are a variety of ways of electricallyconnecting the battery terminals to the bus bars, and that the presentinvention is not limited to any particular scheme. An exemplarytechnique of routing connecting wires between the bus bars and thebattery terminals is shown in FIG. 4. As shown, each of the materials inthe layer stack has an aperture, and the sizes of the apertures arearranged so that a bond wire 401 is less likely to short out to one ofthe bus bars. In the exemplary embodiment, a bus bar on the first layer330 of the layer stack has an aperture 403 through which the bond wire401 passes. An insulator on the second layer 332 of the layer stack hasa smaller aperture 405 through which bond wire 401 passes. A bus bar onthe third layer 334 of the layer stack has a larger aperture 407 throughwhich bond wire 401 passes. The smaller aperture 405 of the insulator,i.e., second layer 332, constrains motion of the bond wire 401 so thatthe bond wire 401 is less likely to contact edges of larger apertures403 or 407. In other words, the bond wire 401 is less likely to contactthe bus bars of the first and third layers as a result of the staggeredaperture sizes. Bond wire 401 couples the bus bar on the first layer 330to a surface 409 of the battery, e.g., a positive or negative terminalat the top of the battery. The apertures within the layers may becircular or any other shape.

FIG. 5 shows a battery holder 500 that may be used with the presentinvention, although it should be understood that the present inventionis not limited to a specific configuration or form factor for thebattery holder. Battery holder 500, which may be molded, cast, printedusing a 3D printer, or fabricated using an alternate technique, ispreferably fabricated from a plastic (polycarbonate, acrylonitrilebutadiene styrene (ABS), polypropylene (PP), polyethylene (PE),polyethylene terephthalate (PET), nylon, etc.), although other materialsmay also be used to fabricate the holder. The battery holder may befabricated as a single piece, a two-piece assembly, a three-pieceassembly, or other configuration. In the illustrated battery holder, thebatteries 502 are inserted into a lower housing member 504, after whichthe upper housing member 506 is attached, for example using one or morefasteners 508 or other means. The battery holder 500 retains thebatteries within the desired battery arrangement, for example in aclose-packed or dense-packed, staggered row or hexagonal configuration.Note that the exemplary battery holder shown in FIG. 5 is only partiallypopulated with batteries.

FIG. 6 provides a schematic illustration of an alternate bus barconfiguration, similar to that shown in FIG. 3, modified to provide amore compact and robust design. Details regarding this configuration,other than for those provided herein, are disclosed in co-pending andco-assigned U.S. patent application Ser. No. 14/203,874, filed 11 Mar.2014, the disclosure of which is incorporated herein for any and allpurposes.

In the configuration illustrated in FIG. 6, the left-most bus bar 601represents the positive terminal of the battery pack while theright-most bus bar 603 represents the negative terminal of the batterypack. In between the two output terminals 601 and 603 are a plurality ofshaped bus bars (e.g., exemplary bus bars 605A-605D). Each shaped busbar 605A-605D includes a lower segment 607 and an upper segment 609,where segments 607 and 609 are connected by a step segment 611fabricated into the bus bar. The stepped feature integrated into eachbus bar 605A-605D allows the bus bars to be stacked together, separatedby an electrical insulator 613. Electrical insulator 613 may becomprised of a layer of electrically insulating material deposited orotherwise applied to one or more outer bus bar surfaces.

In bus bar configuration 600, batteries 615 are connected in parallelsuch that each positive terminal of each battery 615 is coupled tooutput terminal 601 and each negative terminal of each battery 615 iscoupled to the lower segment of bus bar 605A. Similarly, batteries 617are connected in parallel such that each positive terminal of eachbattery 617 is coupled to the upper segment of bus bar 605A and eachnegative terminal of each battery 617 is coupled to the lower segment ofbus bar 605B; batteries 619 are connected in parallel such that eachpositive terminal of each battery 619 is coupled to the upper segment ofbus bar 605B and each negative terminal of each battery 619 is coupledto the lower segment of bus bar 605C; batteries 621 are connected inparallel such that each positive terminal of each battery 621 is coupledto the upper segment of bus bar 605C and each negative terminal of eachbattery 621 is coupled to the lower segment of bus bar 605D; andbatteries 623 are connected in parallel such that each positive terminalof each battery 623 is coupled to the upper segment of bus bar 605D andeach negative terminal of each battery 623 is coupled to the negativeoutput terminal 603. Bus bar 605A serially connects batteries 615 tobatteries 617; bus bar 605B serially connects batteries 617 to 619; busbar 605C serially connects batteries 619 to 621; and bus bar 605Dserially connects batteries 621 to batteries 623. It will be appreciatedthat other battery combinations may be used with this bus barconfiguration, for example utilizing more batteries within each parallelconnected battery group and/or more groups of batteries within the pack.

As in the embodiment shown in FIG. 3, a heat sink 301 is preferablycoupled to the lower end portion of each of the batteries.

In accordance with the invention, in a battery assembly such as thatdescribed above (e.g., assembly 600) in which groups of batteries areelectrically connected in parallel, and where the individual groups areelectrically connected in series, the heat sink that is thermallycoupled to the lower end portion of each of the batteries is segmented.As shown in the exemplary embodiment of FIG. 7, the heat sink issegregated into a series of electrically isolated heat sinks 701-705,where all of the batteries that are immediately adjacent to a particularheat sink segment are of the same, or approximately the same, voltage.Preferably heat sink segments 701-705 are fabricated from a thermallyconductive metal, such as aluminum, although other thermally conductivematerials may be used. The lowermost surface of each battery, and morepreferably the lower portion of each battery, is thermally coupled tothe heat sink segments 701-705 using a layer 707 of a thermallyconductive material, where the selected material preferably has athermal conductivity of at least 0.75 Wm⁻¹K⁻¹ and where the heat sinksegments have a thermal conductivity of at least 100 Wm⁻¹K⁻¹. In atleast one preferred embodiment, layer 707 is fabricated using an epoxy,although the inventors envision the use of other materials as well(e.g., a ceramic). It will be appreciated that heat withdrawal from thebatteries is enhanced by thermally coupling the lower portion of eachbattery to the heat sink segments via layer 707 of the thermallyconductive material as shown, rather than simply interposing a layer ofsuch material in the gap 709 between the bottom surface of each batteryand the heat sink segments. Preferably gap 709 is on the order of 1millimeter. Layer 707, which is in contact with multiple batteries aswell as the heat sink segments, must be comprised of an electricallynon-conductive material, preferably with a resistivity of at least 10¹²ohm-cm, in order to prevent the batteries from shorting to theunderlying heat sink segment. Although not required, in at least oneconfiguration of the invention, and as described in detail in co-pendingand co-assigned U.S. patent application Ser. No. 14/331,300 thedisclosure of which is incorporated herein for any and all purposes, aplurality of electrically non-conductive granules, for examplefabricated from alumina or silica, are dispersed within layer 707, andspecifically within region 709. As a result of the granules, even iflayer 707 softens, the granules help prevent the batteries fromcontacting the underlying heat sink segment.

Mounted beneath heat sink segments 701-705, and interposed between theheat sink segments and a battery pack enclosure lower panel 711, is coldplate 713. Preferably cold plate 713 is fabricated from a metal (e.g.,aluminum), although other materials with a high thermal conductivity mayalso be used. Preferably the thermal conductivity of cold plate 713 isat least 100 Wm⁻¹K⁻¹. Cold plate 713 is used to transfer heat out of thebattery pack, or into the battery pack when battery heating is required.Although cold plate 713 may be air cooled, preferably it is thermallycoupled to one or more coolant conduits 715. In the illustratedembodiment, conduit 715 is incorporated into the cold plate. Interposedbetween the heat sink segments 701-705 and the cold plate 713 is a layer717 of an electrically insulating, thermally conductive interfacematerial. Layer 717 may be continuous as shown, or segmented, althoughif it is segmented than preferably the entire lower surface of each heatsink segment (e.g., segments 701-705) is in thermal contact with athermal layer segment, thus insuring efficient transfer of thermalenergy from the batteries, via the heat sink segments, to the cold plate713. In order to efficiently transfer thermal energy between the heatsink segments and the cold plate, layer (or layers) 717 must have arelatively high thermal conductivity, preferably on the order of atleast 0.75 Wm⁻¹K⁻¹, more preferably of at least 2.0 Wm⁻¹K⁻¹, still morepreferably of at least 5.0 Wm⁻¹K⁻¹, yet still more preferably of atleast 10.0 Wm⁻¹K⁻¹, and yet still more preferably of at least 20.0Wm⁻¹K⁻¹. The material comprising layer (or layers) 717 is selected tohave a relatively high electrical resistivity, preferably on the orderof at least 10¹² ohm-cm, thus electrically isolating the heat sinksegments from the underlying cold plate 713. Regions 719, which separateadjacent heat sink segments, are also selected to have a relatively highelectrical resistivity, preferably on the order of at least 10¹² ohm-cm,thus electrically isolating adjacent heat sink segments. Note thatregions 719 may either be left un-filled, thus allowing air to act asthe electrical insulator, or filled with an electrically insulativematerial.

In the embodiment shown in FIG. 7, heat is transferred from thebatteries to the heat transfer liquid (i.e., coolant) within conduits715 via heat sink segments 701-705, thermal interface material 717, andcold plate 713. The heat is then withdrawn from the battery assembly bythe coolant within conduits 715. Note that in the illustrated andpreferred embodiment, cooling conduits 715 are aligned with lower panel711, resulting in the coolant within channels 715 flowing in a directionsubstantially perpendicular to the axes of the cylindrical batteries. Byregulating the flow of coolant within conduits 715 and/or regulating thetransfer of heat from the coolant to another temperature control system,the temperature of the batteries may be regulated so that they remainwithin their preferred operating range.

By segmenting the heat sink, different voltage groups remainelectrically isolated from one another even if layer 707 fails andallows the batteries to short to the underlying heat sink segments. Forexample, in the battery assembly shown in FIG. 7 where batteries 615 areat a first voltage, batteries 617 are at a second voltage, batteries 619are at a third voltage, batteries 621 are at a fourth voltage, andbatteries 623 are at a fifth voltage, these different battery groupingsremain electrically isolated even if layer 707 fails and allows batteryshorting. As a result, the risk of arcing during a failure of layer 707is reduced, thereby significantly decreasing the risk of a catastrophicevent such as a vehicle fire due to battery arcing. Note that layer 717,which is comprised of an electrically insulative, thermally conductivematerial as described above, prevents the heat sink segments fromshorting to cold plate 713 in the event that layer 707 should fail.

FIG. 8 provides a cross-sectional view of a lower portion of batteryassembly 700, this view taken along plane A-A shown in FIG. 7. Batteries619, which all are of the same or approximately the same voltage, arethermally coupled to a single heat sink segment 703 via layer 707.Thermally coupled to heat sink segment 703 is cold plate 713. Interposedbetween heat sink segment 703 and cold plate 713 is thermal interfacelayer 717, this layer being thermally conductive and electricallyinsulating as noted above. Incorporate into cold plate 713 are multiplecoolant conduits 715. This configuration achieves multiple goals. First,and as described above in detail, if layer 707 fails and allows some orall of the batteries to short to the underlying heat sink segments, themulti-segmented heat sink approach of the present invention in whichheat sink segments are electrically isolated from one another prevents afirst battery group at a first voltage from shorting to a second batterygroup that is at a second, different voltage. Second, by withdrawingheat from the bottom of the batteries using the underlying heat sinks,heat is both transferred between batteries, thereby helping to preventhot spots, as well as between the batteries and the thermal managementsystem to which conduits 715 are coupled. Thus, for example, if abattery such as “Battery A” of FIG. 8 starts to become hotter than theother batteries within the same group, heat will be transferred to thecooler batteries via heat sink segment 703. Additionally, the heat willbe transferred to multiple conduits 715. Note that this is in markedcontrast to a battery assembly configuration such as that shown in FIG.2 in which the cooling conduits are located between adjacent batteries,thereby limiting the transfer of thermal energy between batteries aswell as to the thermal management system.

FIGS. 9 and 10 illustrate exemplary cooling systems that may be coupledto cooling conduits 715. In system 900 shown in FIG. 9, the coolantwithin conduits 715 is pumped through a radiator 901 using a pump 903. Ablower fan 905 may be used to force air through radiator 901 to insurecooling when the car is stationary. In system 1000 shown in FIG. 10, thecoolant within conduits 715 is coupled to a thermal management system1001 via a heat exchanger 1003. Preferably thermal management system1001 is a refrigeration system and as such, includes a compressor 1005to compress the low temperature vapor in refrigerant line 1007 into ahigh temperature vapor and a condenser 1009 in which a portion of thecaptured heat is dissipated. After passing through condenser 1009, therefrigerant changes phases from vapor to liquid, the liquid remaining ata temperature below the saturation temperature at the prevailingpressure. The refrigerant then passes through a dryer 1011 that removesmoisture from the condensed refrigerant. After dryer 1011, refrigerantline 1007 is coupled to heat exchanger 1003 via thermal expansion valve1013 which controls the flow rate of refrigerant into heat exchanger1003. Additionally, in the illustrated system a blower fan 1015 is usedin conjunction with condenser 1009 to improve system efficiency. Itshould be understood that battery pack coolant conduits 715 may becoupled to other cooling/thermal management systems, and the coolingsystems shown in FIGS. 9 and 10 are only meant to illustrate some commonconfigurations for use with the conduits of the invention. Additionally,the geometry of cooling conduits 715 shown in FIGS. 9 and 10 is onlymeant to illustrate one possible configuration.

FIGS. 11-13 provide cross-sectional views, similar to those of FIGS. 7and 8, of an alternate embodiment of the invention. As in the priorembodiment, the battery assembly includes a plurality of batteriesdivided into battery groups, where the batteries within each group areelectrically connected in parallel and are of the same voltage, whereindividual battery groups are electrically connected in series, andwhere each group of batteries is at a different voltage than the otherbattery groups. Also as in the prior embodiment, the heat sink that isthermally coupled to the lower end portion of each of the batteries issegmented. In assembly 1100, the heat sink is segregated into a seriesof electrically isolated heat sinks 1101-1105, where all of thebatteries that are immediately adjacent to a particular heat sinksegment are of the same, or approximately the same, voltage. Heat sinksegments 1101-1105 are fabricated from a thermally conductive material,for example a metal such as aluminum, which preferably has a thermalconductivity of at least 100 Wm⁻¹K⁻¹. The lowermost surface of eachbattery, and more preferably the lower portion of each battery, isthermally coupled to the heat sink segments 1101-1105 via a thermallyconductive layer 707 (e.g., an epoxy layer), where layer 707 preferablyhas a thermal conductivity of at least 0.75 Wm⁻¹K⁻¹. As in the priorembodiment, layer 707 is comprised of an electrically non-conductivematerial, preferably with a resistivity of at least 10¹² ohm-cm.

Unlike battery assembly 700 which utilizes a cold plate 713 that isthermally coupled to, but electrically isolated from, the heat sinksegments, assembly 1100 utilizes heat sink segments that serve dualpurposes; first as a heat sink and heat spreader, and second as a coldplate that transfers heat out of the battery pack or transfers heat intothe battery pack when battery heating is required. As such, a conduit1107 is incorporated into, and passes through, each of the heat sinksegments. Although conduit 1107 may be arranged orthogonally from theconfiguration shown in FIGS. 11 and 12, the illustrated configuration ispreferred as it helps to further stabilize battery temperature byefficiently transferring heat between heat sink segments. Interposedbetween the heat sink segments 1101-1105 and the coolant conduit 1107 isa layer 1109 of an electrically insulating, thermally conductiveinterface material. Layer 1109 is preferably comprised of a coatingapplied to the exterior surface of conduit 1107, although in at leastone embodiment layer 1109 is comprised of a tube of appropriate material(i.e., an electrically insulating and thermally conductive material)which electrically isolates conduit 1107 from the heat sink segments.Other configurations for layer 1109 are also envisioned (e.g., a coatingapplied to the interface surface of the heat sink segments). In order toefficiently transfer thermal energy between the heat sink segments andthe coolant contained within conduit 1107, layer 1109 must have arelatively high thermal conductivity, preferably on the order of atleast 0.75 Wm⁻¹K⁻¹, more preferably of at least 2.0 Wm⁻¹K⁻¹, still morepreferably of at least 5.0 Wm⁻¹K⁻¹, yet still more preferably of atleast 10.0 Wm⁻¹K⁻¹, and yet still more preferably of at least 20.0Wm⁻¹K⁻¹. The material comprising layer 1109 is selected to have arelatively high electrical resistivity, preferably on the order of atleast 10¹² ohm-cm, thus electrically isolating the heat sink segmentsfrom each other. The material comprising regions 1111, which separateadjacent heat sink segments, is also selected to have a relatively highelectrical resistivity, preferably on the order of at least 10¹² ohm-cm,thus electrically isolating adjacent heat sink segments. Note thatregions 1111 may either be left un-filled, thus allowing air to act asthe electrical insulator, or filled with an electrically insulativematerial.

Assembly 1100 functions in much the same way as assembly 700.Specifically, heat is transferred from the batteries to the heattransfer liquid (i.e., coolant) within conduits 1107 via heat sinksegments 1101-1105 and thermal interface layer 1109. The heat is thenwithdrawn from the battery assembly by the coolant within conduits 1107.By segmenting the heat sink, different voltage groups remainelectrically isolated from one another even if layer 707 fails and thebatteries short to the underlying heat sink segments. As a result, therisk of arcing and the ensuing catastrophic event are minimized.

FIG. 12 provides a cross-sectional view of a lower portion of batteryassembly 1100, this view taken along plane B-B shown in FIG. 11. Thisview highlights the incorporation of cooling conduits 1107 within theheat sink segments, specifically heat sink segment 1103 in this view.Batteries 619, which are of the same or approximately the same voltage,are thermally coupled to single heat sink segment 1103 via layer 707.Also visible in this view are the thermal interface layers 1109 thatelectrically isolate the coolant conduits 1107 from heat sink segment1103.

FIG. 13 provides a cross-sectional view of battery assembly 1100 inwhich the heat sink segments have been modified to simplify insertion ofthe coolant conduits 1107 and the accompanying thermal interface layer1109 into the heat sink segments. As shown, the bottom portion of theheat sink segment is slotted to accommodate conduits 1107. Fingers 1301may be sized to allow conduits 1107 and the accompanying thermalinterface layer 1109 to ‘snap’ into the heat sink segments. Alternately,fingers 1301 may be crimped after insertion of the coolant conduit 1107and the thermal interface layer 1109, the crimping holding the conduitsfirmly in place in order to insure the efficient transfer of thermalenergy between the coolant conduits and the heat sink segments. It willbe appreciated that other techniques, such as bonding, may also be usedto hold the conduits in place within the slots. Additionally, it shouldbe understood that the use of slots to hold the coolant conduits inplace may also be used with the previous embodiment, i.e., the bottomsurface of cold plate 713 may be slotted to accommodate coolant conduits715.

FIGS. 14-16 provide similar views as those provided by FIGS. 11-13 for abattery assembly that utilizes electrically insulative conduits 1401,thereby eliminating the need for a thermal interface layer (e.g., layer1109) between the conduits and the heat sink segments. Preferablyconduits 1401 have a relatively high thermal conductivity, on the orderof at least 0.75 Wm⁻¹K⁻¹, more preferably of at least 2.0 Wm⁻¹K⁻¹, stillmore preferably of at least 5.0 Wm⁻¹K⁻¹, yet still more preferably of atleast 10.0 Wm⁻¹K⁻¹, and yet still more preferably of at least 20.0Wm⁻¹K⁻¹. Additionally, the conduits are fabricated from a material witha relatively high electrical resistivity, preferably on the order of atleast 10¹² ohm-cm, thus electrically isolating the heat sink segmentsfrom one another. In at least one embodiment conduits 1401 arefabricated from a plastic polymer material (e.g., polyethylene,polypropylene, etc.) which, if desired, may be treated to improvethermal conductivity while still retaining its electricallynon-conductive properties.

FIG. 17 provides a bottom view of a portion of a battery assembly, suchas those shown in the above figures, this view illustrating thepreferred orientation of the coolant conduits 1701 relative to the heatsink segments 1703-1706. For clarity, the electrical isolation barrier1707 is shown between the heat sink segments. Note that batteries 1709are shown in phantom (i.e., dashed lines). This view illustrates how abattery assembly configured in accordance with the invention spreadsheat throughout the assembly, thereby allowing a ‘hot’ battery (e.g.,battery 1711) to transfer its thermal energy to multiple batteries andmultiple coolant conduits, rather than relying on the transfer of heatonly to an immediately adjacent battery and/or coolant conduit.

Systems and methods have been described in general terms as an aid tounderstanding details of the invention. In some instances, well-knownstructures, materials, and/or operations have not been specificallyshown or described in detail to avoid obscuring aspects of theinvention. In other instances, specific details have been given in orderto provide a thorough understanding of the invention. One skilled in therelevant art will recognize that the invention may be embodied in otherspecific forms, for example to adapt to a particular system or apparatusor situation or material or component, without departing from the spiritor essential characteristics thereof. Therefore the disclosures anddescriptions herein are intended to be illustrative, but not limiting,of the scope of the invention.

What is claimed is:
 1. A battery assembly, comprising: a plurality of batteries, each battery of said plurality of batteries comprising a first terminal at a first end portion of said battery and a second terminal at said first end portion of said battery, wherein said plurality of batteries are divided into a plurality of battery groups, wherein each battery group of said plurality of battery groups comprises a subset of said plurality of batteries, wherein said batteries within each subset of said plurality of batteries are electrically connected in parallel, wherein said batteries within each subset of said plurality of batteries are maintained at a different voltage than every other subset of said plurality of batteries, and wherein said battery groups of said plurality of battery groups are electrically connected in series; and a plurality of bus bars positioned proximate to said first end portion of each of said plurality of batteries, wherein said plurality of bus bars are electrically connected to said first and second terminals of each battery of said plurality of batteries; a plurality of heat sink segments, wherein each heat sink segment of said plurality of heat sink segments is electrically isolated from adjacent heat sink segments, wherein each heat sink segment of said plurality of heat sink segments is thermally coupled to one battery group of said plurality of battery groups such that a second end portion of each battery of each battery group is thermally coupled to one heat sink segment of said plurality of heat sink segments, and wherein said second end portion of each battery of said plurality of batteries is distal from said first end portion of each battery of said plurality of batteries; a cold plate thermally coupled to said plurality of heat sink segments; and a layer of a thermal interface material interposed between said cold plate and each of said plurality of heat sink segments, wherein said thermal interface material is thermally conductive and electrically insulative.
 2. The battery assembly of claim 1, further comprising a thermally conductive material layer interposed between said second end portion of each battery of each battery group and a corresponding heat sink segment of said plurality of heat sink segments, wherein said thermally conductive material layer is electrically insulative.
 3. The battery assembly of claim 2, wherein said thermally conductive material layer contacts and is thermally coupled to a lower portion of each battery of said plurality of batteries.
 4. The battery assembly of claim 2, wherein said thermally conductive material layer has a thermal conductivity of at least 0.75 Wm⁻¹K⁻¹ and a resistivity of at least 10¹² ohm-cm.
 5. The battery assembly of claim 2, wherein said thermally conductive material layer is comprised of a material selected from the group consisting of epoxies and ceramics.
 6. The battery assembly of claim 1, further comprising an electrically insulative material interposed between each heat sink segment of said plurality of heat sink segments and said adjacent heat sink segments.
 7. The battery assembly of claim 6, wherein said electrically insulative material interposed between each heat sink segment of said plurality of heat sink segments and said adjacent heat sink segment is comprised of a material with a resistivity of at least 10¹² ohm-cm.
 8. The battery assembly of claim 1, further comprising at least one coolant conduit thermally coupled to said cold plate.
 9. The battery assembly of claim 8, wherein said at least one coolant conduit is integrated into said cold plate.
 10. The battery assembly of claim 9, wherein a surface of said cold plate is slotted to accommodate said at least one coolant conduit.
 11. The battery assembly of claim 8, wherein said at least one coolant conduit is coupled to a battery pack thermal management system.
 12. The battery assembly of claim 1, wherein said layer of said thermal interface material has a thermal conductivity of at least 0.75 Wm⁻¹K⁻¹ and a resistivity of at least 10¹² ohm-cm.
 13. The battery assembly of claim 12, wherein said thermal conductivity of said layer of said thermal interface material is at least 5.0 Wm⁻¹K⁻¹.
 14. The battery assembly of claim 13, wherein said thermal conductivity of said layer of said thermal interface material is at least 20.0 Wm⁻¹K⁻¹.
 15. The battery assembly of claim 1, wherein each heat sink segment of said plurality of heat sink segments is comprised of a metal.
 16. The battery assembly of claim 15, wherein each heat sink segment of said plurality of heat sink segments is comprised of aluminum.
 17. The battery assembly of claim 1, wherein each heat sink segment of said plurality of heat sink segments has a thermal conductivity of at least 100 Wm⁻¹K⁻¹.
 18. The battery assembly of claim 1, wherein said cold plate is comprised of a metal.
 19. The battery assembly of claim 18, wherein said cold plate is comprised of aluminum.
 20. The battery assembly of claim 1, wherein cold plate has a thermal conductivity of at least 100 Wm⁻¹K⁻¹. 